1. Field of the Invention
The present invention relates to a structure of a switch device.
2. Description of the Related Art
There is conventionally used a device in which an operator lifts up or pushes down one end of a knob to switch contact points, as a switch device suitable for an operation of powered windows in an automobile or the like. This kind of switch devices, as disclosed, for example, in Japanese Patent Laid-Open Publication No. 2003-77370, are designed to perform a switching operation by sliding a slider engaging to a predetermined section of a swing knob. FIG. 12 is a cross section showing the structure of the above-mentioned conventional switch device. Major components in the switch device 100 are incorporated in a plastic case comprising an upper case 105 and a lower case 110.
A knob 102 provided with a lever 103 extending downward is swingably supported by the upper case 105. The upper case 105 is coupled to the lower case 110 at an unillustrated section thereof. Electrode plates 130, 131, and 132 arrayed in a line are arranged on a bottom wall 111 of the lower case 110. Contact points 134 and 135 are respectively provided in the electrode plates 130 and 132 at both the ends. The central electrode plate 131 rises up from the bottom wall 111 to support a swing contact piece 127. The swing contact piece 127 is arrange along the line of the electrode plates 130, 131, and 132, and the electrode plate 131 supports an approximately intermediate position of the swing contact piece 127.
An accommodating wall 113 rises up from the bottom wall 111 to surround the electrode plates 130, 131 and 132, and the swing contact piece 127 to form a contact point accommodating chamber S′, and a slider cover 115 provided with a window 116 for insertion of a slider 120 in the central part is mounted to an upward opening portion of the contact point accommodating chamber S′. The slider 120 comprises a head portion 121 engaging to the lever 103 of the knob 102 above the slider cover 115, a tubular portion 122 extending downward through the window 116 of the slider cover 115 from the head portion 121, and a slider plate portion 123 extending in a perpendicular direction to an axis of the tubular portion 112 from the halfway thereof. The tubular portion 122 accommodates a coil spring 124 therein, retains a ball 125 at an opening portion of the tubular portion 122 in a lower end thereof, and presses the ball 125 urged by the coil spring 124 to the swing contact piece 127. The slider 120 is guided by forcing the slider plate portion 123 to move along the lower surface of the slider cover 115, and is provided to be slidable in the front-back direction (right-left direction in the figure).
The swing contact piece 127 is provided with a click portion 128 having a cam shape, and the ball 125 makes contact with the click portion 128. The click portion 128 is provided with the lowest portion of the trough in a position closer to the contact point 134 than a support position by the electrode plate 131. FIG. 12 shows a state where the slider 120 is in a neutral position. In the neutral position, the ball 125 presses the lowest portion of the trough in the click portion 128, so that one end of the swing contact piece 127 is seated on the contact point 134 and the other end is separated from the contact point 135.
When the front end of the knob 102 is pressed, the lever 103 swings in a counterclockwise direction to move the slider 120 from the neutral position to the backward side (right direction in the figure). Thereby without any change in a posture of the swing contact piece 127 supported by the contact point 134 and the electrode plate 131, the ball 125 compresses the coil spring 124, while following the cam shape of the click portion 128. Accordingly, there is no change in an electrical connection state where electricity flows between the contact point 134 and the electrode plate 131. On the other hand, when the front end of the knob 102 is lifted up, the lever 103 swings in a clockwise direction to move the slider 120 from the neutral position to the forward side (left direction in the figure). Accordingly, the ball 125 moves in a direction of the contact point 135 on the click portion 128. As the ball 125 exceeds the support position by the electrode plate 131, since the swing contact piece 127 is made to swing in a counterclockwise direction, one end of the swing contact piece 127 is away from the contact point 134, and the other end is seated on the contact point 135. As a result, the electrical connection state is switched to establish an electrical connection between the electrode plate 131 and the contact point 135.
Incidentally in the switch device, adherence of foreign objects such as dusts to the contact point causes an operational defect. Therefore according to the above-mentioned conventional example, also in a case where the slider 120 moves from the neutral position to the forward side and the backward side respectively, a size of the slider plate portion 123 is set in such a manner as to close the window 116 of the slider cover 115. In this manner, the conventional switch device is designed to prevent the foreign object from entering into the contact point accommodating chamber S′ where the electrode plates 130, 131, and 132, and the swing contact piece 127 are positioned.
However, since the slider plate portion 123 is positioned at the lower surface side of the slider cover 115, in a case where foreign objects drop and are accumulated on a section of the slider plate portion 123 exposed to the window 116, the foreign object enters into a gap between the lower surface of the slider cover 115 and the slider plate portion 123 to block a smooth slide of the slider plate portion 123, and further, the foreign object drops off from a peripheral edge of the slider plate portion 123 by repetition of the sliding, creating a possibility that the foreign object enters into the contact point accommodating chamber S′. In addition, only with the aim at guiding the slide of the slider 120 in the first place, although it is only required to form a guide groove in the accommodating wall 113, the slider cover 115 as a component different from the lower case 110 or the upper case 105 is mounted for prevention of the entering of the foreign object. Therefore the conventional switch device has room for further improvement on a point of causing an increase in component costs and mounting man-hours.
For overcoming this problem, for example, as shown in FIG. 13, it is considered to structure a switch device as follows. A slider plate portion 123′ of a slider 120′ is sized to cover the entirety of the contact point accommodating chamber S′, a flange wall 118 extending downward is provided to a peripheral edge of the slider plate portion 123′, and the slider 120′ covers an accommodating wall 113′ to slide thereon, thus abolishing the slider cover 115. However, since the slider 120′ slides in the front side and in the back side to the contact point accommodating chamber S′, in this case since a predetermined gap K for absorbing a slide amount of the slider 120′ is required at each of the front and back sides between the flange wall 118 and an outer surface of the accommodating wall 113′, the slider plate portion 123′ of the slider 120′ is sized to be larger by the amount of the gaps, requiring a large space for its installation. In a case of providing this kind of switch devices to a driver's seat door in an automobile, at least four switch devices are arranged in an arm rest of the door for controlling powered windows in a sedan type of automobiles. However, there is an increasing demand for arranging many switch devices for angular adjustment, and storage/development of door mirrors, door locks, and the like in the arm rest in addition to the above powered window. However, since a space in the arm rest for installation of the switch device is limited, downsizing each of the switch devices is inevitable for meeting the demand for arranging many switch devices in the arm rest. The slider requiring a large space for its installation is not practical in this respect.